1. Field of the Invention
The invention relates to a Programmable Logic Controller system (which will hereinafter be referred to as a “PLC system”).
2. Description of the Related Art
A PLC system is made of various expansion units such as an I/O unit and a D/A conversion unit as well as a CPU unit. The models and the number of the expansion units are determined as desiredby the operator. The preparation of a control program of the PLC system and various settings for each expansion unit are executed, for example, using a sequence programming tool such as ladder chart creation support software with an external computer.
Japanese Patent Unexamined Publication No. Hei. 5-241623 and Japanese Patent Unexamined Publication No. Hei. 9-16220, propose that an expansion unit such as an I/O unit is provided with display means for blinking LED to check wiring in a constructed PLC system or check the operation of a control system or that a special indicator is connected to a PLC system for checking the I/O state.
In the PLC system in the related art, for example, to check the setting for each expansion unit or when an operation failure is found, generally programs and various settings stored in an external computer are checked, the setup values are corrected using a sequence programming tool such as ladder chart creation support software installed in the computer, and then the corrected programs, and the like, are again down loaded into a CPU unit of the PLC system, and the operation of the PLC system is again checked. Such a process is intricate.